Signaling



J y 1929- .1; F. FARRINGTON 1,722,030

- SIGNALING Filed Dec. 31, 1923 John E Farr/Hymn. fly

Patented July 23, 1%29;

ll t l i iii E S emg; Fir-a e;

trail n JOHN F. FABRING'EON, 0F FLUSHING, NEW YGRK, ASSEGNOE 'lO WESTERN ELECTRIC COMPANY, INCORPGRATED, 6F NEW" YORK, N. Y A GOBP JRATIGN OF NEW srennmive- Application filed December 31, 1923. Serial ad. ceas s.

This invention relates to twoway signal ing systems and as illustrated in the embodiment herein described, it is particularly adapted for use in radio telephone systems.

The development of twoway radio or other types of high frequency systems has been a ttended by Considerable dilliculty, principally on account of the excessive influence of the transmitter upon the local receiver at each station. These difficulties ar inherently greater in high frequency than in low frequency signaling systems on account of the relatively greater effect-s resulting from the presence ofdistributed, or ther forms ot casual and unpreventable capacity in high frequency systems. These diliiculties are nherently greater for radio systems thanror wire systems on account of the relat vely greater difierence between the transm tted and received energies in the former, and the consequently greater difference in the sensitivity of the respective transmitting and receiving apparatus when arranged for efiicient operation.

The problem has been met in practice in a variety of ways, the essential feature of each of which is a means for preventing energy from the transmitter from flowing in the local receiver circuit. Means employed, having this desired result in mind, include: the use of circuit arrangements for switching a common antenna from the transmitting to the receiving set so that transmission and reception can be carried on alternately; balanced circuit arrangements for transmitting energy to a common antenna without affecting the local receiving circuit; and particular relative arragements of individual transn'ntting and receiving antennae invplying special geographical or geometrical relation. I

By the arrangement of the present nvention a similar result is accomp ied Without the necessity of completely preventing the transmitted wave from acting on the local receiver. In. fact, in this arrangement, a certain amount of this energy is utilized in the receiver circuit, for example, to produce amplification of the signal and to increase the discriminating power of the receiving 011'- cuit with respect to the frequencies of nudesired waves which are incident on the antenna. The arrangement of the invention is accordingly simpler and less expensive than certain prior systems, which require greater elaboration of circuits inorder to avoid the presence of these interfering currents in the receiver. 7

An object of the invention is therefore, broadly, to provide improved methods of and means for two way signaling, and more specifically for two-way radio signaling.

A particular object is to provide a two-way system in'which the locally produced carrier wave for the outgoing transmission aids in selecting and amplifying the incoming signal wave and thereby, to a considerable extent, overcomes the effect of interfering Waves.

A further object is to provide a system in which an operative condition of the local transmitting or receiving circuits, or those at a distant station, will be indicated to the operator at the local station. The absence of side tone effect will warn the operator that the apparatus is not functioning properly.

A further object is to provide improved methods of two-Way communication in which a single element such as an oscillator of a transmission circuit may function usefully as an element of the receiver circuit.

A still further object is to reduce the number of vacuum tubes employed in two-way communication systems. I

These objects are realized in arrangements in which the received energy and a certain amount of energy of the outgoing carrier frequencies are combined and detected, a local auxiliary current Wave being thereby produced, This current of auxiliary carrier frequency is modulated or varied in amplitude in accordance with both the outgoing and incoming signals and by detecting it, a wave will be produced from which may be derived both the incoming, and outgoing signals. The auxiliary carrier frequency may be equal'to either the sum or difference of the principal carrier'frequencies, but since many practical advantages attend the use of the difference, rather than the sum frequency, this is the one which maybe most'convenient- 1y utilized. The amplitude of the auxiliary carrier frequency current will be proportionalto the product of the amplitudes of the local and distant carriers. 'lhus, assuming the same percentage of modulation at each station, a signal in the local receiver will be of approximately the same intensity Whether the localor distant station is transmitting. In order to obtain a maximum indication from a distant'station, it is consequently de oscillator and the detector are combined in a single structure. In particular the system of this invention differs from that of similar systems invented by applicant, namely, the one disclosed in British Patent 186,9a6, in that the grid-filament path of the transmitting oscillator is used to detect the incoming wave. 1

Further objects of the invention Will be apparent to those skilled in the art from a consideration of the following detailed description with reference to the accompanying drawings in Which the single figure illustrates one system embodying the principle of the invention.

Referring to this figure, the signal frequency source 1, modulator M, oscillator O, and antenna AN, cooperate to generate and radiate a high frequency signal modulated carrier Wave Which may be symbolically represented by f f s in which 7, is the frequency of the unmodulated carrier and his, indicates the signal side bands. Carrier frequency f,, may in a practical case, be of the order of 500,000 cycles. Antenna AN is tuned to the mean frequency of the radiated Wave by variable condenser 2 and the inductance 13. Branch circuit 3 is utilized for tuning the antenna to the frequency of an incoming Wave, as Will be later described. Loop resonant circuit 1 in this branch is tuned to the mean frequency of the transmitted Wave and accordingly interposes in this branch .a substantially infinite impedance to the transmitted current, effectively eliminating it so far as concerns the operation of the system during transmission. 0

The modulator system is of the kind commonly denominated constant current modulation which is illustrated and described, for example, in U. S. patent to Sehelleng No. 1,437,021, issued November 28, 1922. Other functionally equivalent systems may equally Well be used. The oscillator of the system il-. lustrated is of the Colpitts type described,

for example, inU. S. patent to Colpitts 1,624,- 537, granted April 12', 1927. A distinguishing feature of its circuit is the connection of the electric discharge device comprising one of these elements to the antenna in such a manner that the antenna itself constitutes the frequency determining circuit of the oscillator. The plate circuit of the device is supplied from a direct current source 5, through low frequency choke 6. Modulator M is, in effect, a device of impedance variable at si 'nal frequencies by virtue of the operation of the microphone circuit 1. Its function is to cause'a variable flow of current through the space path of the tube of the oscillator O in response to and in accordance with impressed signal frequency variations, and accordingly, on account of the resultant potential drop in choke coil 6, to cause a corresponding variation in the inverse direction of the potential applied to the plate of the oscillator. These low frequency Variations ofthe effective plate potential of the oscillator are effective to cause corresponding variations or modulations of the generated carrier oscillations. High frequency choke. 7 prevents the high frequency currents of the oscillator from reacting on the low frequency circuits.

The incoming signal modulated Wave is selectively received by the antenna system, which comprises, for this function, the an tenna proper and the branch 3. The block 8 indicates diagrammatically any arrangement of impedance elements required to effect the necessary tuning. The anti-resonant circuit at in branch 3 effectively open-circuits this branch for the transmitted currents. The antenna system is accordingly capable, in effeet, of independently oscillating according to two distinct frequencies and accordingly can efficiently transmit outgoing and select and receive incoming high frequency Waves, simultaneously or successively.

On account of the detecting or demodulating action of the grid-filament circuit of the oscillator, resulting from the curvilinear form of its gridpotential-grid-current characteristic curve, the incoming Waves are combined with the outgoing Waves to produce in circuit 9 a resultant difference frequency Wave. For example, if the desired incoming Wave 7, has a frequency of 530,000 cycles,

and with the value given above for f the detected difference frequency Will have a frequency of 30,000 cycles. If either or both of the additional frequencies f l-S and f is are present in the Waves impressed on the detecting circuit there Will additionally appear in circuit 9 a wave of this difference frequency modulated by S S or both these frequencies, as the case may be. The resultant difterence frequency detected wave may accordingly be represented by the legend f2 f1,f1 f2:l:' i (it is immaterial as to Whether the difference frequency is expressed as f f, or f-, f,).

This Wave is selected by resonant circuits l0 and 12 and impressed on the detector or demodulator DM. Other types of selective circuits such as a filter, may be used instead -in U. S. patent to Heising No. 1,452,389,

issued April 17 1923, to which reference is made. They have been found to provide a leakage discharge path for the negative charges accumulated on the grid of the device which has particular functions when high frequency potentials are impressed which are not realized to the same extent when the conventional resistance aloneis used. However, a resistance may be used in lieu of this particular arrangement.

If it is assumed, as in a practical case, that signals are being transmitted in only one direction at a time, during signal transmission a signal side tone will be heard in the receivers 11. This will indicate an operative condition of the circuit. Nhen signal modulated waves are incoming, the reproduced signal from a distant station will similarly be heard in the receivers. The amplitude of these signals may be greater than that of the signal that could be obtained directly from the first stage of detection, because of the action of the local transmitting energy. An additional amplification can be secured, if desired, by separately amplifying the selected auxiliary frequency component. Since the frequency of the incoming carrier is efiectively reduced by combination with the carrier from the local source there results, by the use of suitable circuits for selecting the modulated difference frequency carrier, better discrimination between two or more carrier waves having nearly the same frequency simultaneously incident on the antenna. Since an indication is received in the telephone receivers during outgoing transmission, upon which an incoming signal indication would be supcrposed if incoming signal transmission simultaneously occurred, the arrangement provides a means whereby the distant operator can break-in on the transmission incoming to him.

Having described a preferred form of the invention, the parts, features and combinations and methods inherent. therein which are believed to be patentable are defined in the appended claims.

What is claimed is:

1. In a two-way signaling system, a transmission channel for transmitting outgoing waves including a three-electrode electric discharge device having a cathode, an anode, and a control electrode and a path including said cathode and control electrode and adapted for utilizing the asymmetrically conducting properties of the circuit therebetween for detecting and reproducing the slgnal represented by the modulating component of the slgnal modulated incoming wave.

2; A signaling system comprising two stations each of which comprises a source of signaling Waves, a high frequency carrier wave source, a three-electrode electric discharge translating device in the outgoing channel, means for combining the energy of each of said carrier waves to produce an intermediate carrier frequency wave, and means for deriving each of said signaling waves from said intermediate carrier frequency wave, said combining means comprising cathode and control elements of said three-electrode electric discharge device and being adapted to I utilize the curvilinear relation between the potentials impressed, and the current flowing, bet-ween said elements.

In a system of two-way signaling, a transmission channel for transmitting outgoing waves including a three-electrode electric discharge device comprising a cathode and a control electrode, and means utilizing the unsymmetrical properties of the cathodecontrol electrode circuit for receiving incoming waves and combining them with energy of the outgoing wave frequency to produce a Wave of carrier frequency modulated in accordance with incoming and outgoing sig nals.

4. In a two-way signaling system, an electric discharge device having input and output electrodes, means for impressing waves to be transmitted upon said output electrodes, means for impressing received waves upon said input electrodes, a circuit connected to said input electrodes including selective means for transferring electric waves having a frequency equal to the difference of the incoming and outgoing wave frequencies, and means for detecting and indicating the selected Waves.

5. In a two-way signaling system, a threeelectrode electric discharge oscillator including coupled input and output circuits and input electrodes, means for varying the impedance of said oscillator in accordance with signals, means for impressing received signal modulated waves upon said input electrodes, means for selecting the detected wave resulting from combination of the incoming and outgoing waves in said input circuit, and

means for detecting said. selected wave andfor indicating the resultant reproduced modulators.

6. In a two-way signaling system, an antenna including an inductance element, an electric discharge oscillator comprising av cathode, an anode, and a control element, means connecting said anode and control electrode to separated points in said antenna including at least a portion of said inductance, means for varying the amplitude of the generated oscillations in accordance With signals, means including said cathode and control electrode for combining incoming and outgoing Waves and for selecting dif ference frequency components resulting from the combination, means for detecting said difference frequency component and means for including the resultant reproduced modulating components of said incoming and outgoing Waves.

In Witness whereof, I hereunto subscribe my name this 26 day of December A; D. 1923.

JOHN F.- FARRINGTON. 

